1. Field of the Invention
The present invention relates to an electromagnetic power transmission clutch, and more particularly to an improved clutch structure in which a magnetic coil is secured in and insulated from a coil housing. The magnetic clutch is suitably applied to a compressor in a vehicle air conditioner.
2. Related Art
A conventional compressor in a vehicle air conditioner is connected to a vehicle engine through a magnetic clutch. The magnetic clutch is used to connect and disconnect the compressor with the engine. JP-A-64-26032 discloses a structure in which a magnetic coil of such a magnetic clutch is secured in a ferrous metal coil housing. In JP-A-64-26032, an adhesive-type insulating tape is wound around an annular electromagnetic coil at a plurality of points along a circumference of the coil to maintain the winding shape of the coil. Therefore, when the coil is inserted into the coil housing, a predetermined gap is provided between a surface of the coil and an inside surface of the coil housing by the insulating tape. Further, the gap is filled with insulating resin so that the magnetic coil is secured in, while being insulated from, the coil housing.
However, in JP-A-64-26032, the number of tape windings must be large, because the gap between the surface of the coil and the inside surface of the coil housing is formed by the insulating tape. If the number of tape windings is small, the resulting thickness of the tape wound around the coil is decreased. In this case, direct contact between a portion of the coil not insulated by the tape and the coil housing may occur due to deformation or irregularity of the coil, resulting in inadequate coil insulation. If the number of tape windings around the coil is increased, manufacturing and materials costs would both increase.